1. Field of the Invention
The present invention relates to an accumulator having a housing and a rod, and more particularly, to a sealing structure at an insertion region of the accumulator through which the rod is inserted into the housing.
2. Description of the Related Art
A conventional shock absorber comprises a housing containing a hydraulic fluid therein, a rod inserted in the housing for axial movement, and a damping force generating mechanism disposed inside the housing. When the housing and the rod move relatively to each other in the axial direction, the fluid flows through the damping force generating mechanism, thereby damping the motion of the rod.
The shock absorber is used in combination with suspension springs of a motor vehicle. In this case, load of the vehicle body is supported by the suspension springs, so that the internal pressure of the housing need not be high. In a hydropneumatic suspension developed by the inventors hereof, however, the housing must be charged with a gas at a very high pressure in order that the vehicle body load is supported by means of the repulsive force of the gas in the housing. In this case, the gas pressure sometimes may attain 100 kgf/cm.sup.2 or more. It is essential, therefore, to securely seal an insertion region at an open end of the housing for the insertion of the rod.
A typical example of the prior art sealing structure comprises an annular groove formed on the inner surface of a housing, in the vicinity of an open end thereof, a plastic seal ring housed in the groove, and an O-ring press-fitted between the outer peripheral surface of the seal ring and the bottom of the annular groove. The section of seal ring in its axial direction is rectangular, and the inner peripheral surface of the seal ring is in contact with the outer peripheral surface of the rod.
If the interference of the seal ring is too great, in the sealing structure described above, the frictional drag of the seal ring against the rod becomes too great, and lubrication of the seal ring is insufficient. In such a case, the rod cannot smoothly move, and the seal ring is liable to wear. If the interference of the seal ring is too small, on the other hand, an excessive, unstable fluid leakage is caused between the rod and the seal ring, especially when the rod moves at high speed.